PA Réalt·Stone and Sky

Solas sa seomra · grianstad an gheimhridhLight in the chamber: Newgrange at the winter solstice

Pick a morning and drag the time slider, or drag across the chart. The Sun’s position is computed for Newgrange. Day zero is the December solstice for the relevant year, from Astronomy Engine, not a fixed 21 December. The gold window is the zone of sky from which direct sunlight was actually photographed in the chamber in 2020–21: the 53 positions measured in the NMS 2024 research report, shown as dots. When the Sun is inside that window, the beam lights the chamber.

One light window is used for Today and for Light this week. National Monuments Service (2024), Winter Solstice Phenomenon at Newgrange: Research Report (F. Prendergast) gives three figures. The key findings (section 2) say the limits are “currently being about 20 days either side of the notional date of the winter solstice on 21 December.” Table 9 says direct sunlight on 8 January 2021 “has effectively ended by this date, 19 days after the notional date of the winter solstice on 21 December 2020,” and that it “will also enter the burial chamber 19 days before solstice, albeit minimally.” Chapter 10 says “direct light from the rising Sun which can only penetrate the chamber for less than 20 minutes for about 18 days either side of the date of the winter solstice.” Today and Light this week follow that chapter 10 figure, 18 calendar days, so they open and close together. Counted back from 21 December, 20, 19 and 18 days are 1, 2 and 3 December, so light may enter from about 1–3 December. The window used here opens on 3 December when the solstice falls on 21 December. Direct sunlight was photographed in the chamber from 12 December 2020 to 8 January 2021.

Spéir na hoíche · an spéir inniuThe sky over Brú na Bóinne

This is the real sky above Newgrange: 2,309 catalogue stars down to magnitude 5.3, with the Sun, Moon and planets computed for the chosen moment. The rim of the dome is the true local horizon, and the gold ticks show where the Sun rises and sets at the solstices and equinoxes.

Éileamh agus fianaiseClaims vs evidence

Some alignments are measured, repeatable and probably intended. Others are beautiful coincidences, or claims that fell apart when surveyed. Each card gives the claim, what was measured and our reading of it, with links to the sources.

• Strong measured, repeatable, widely accepted
• Observed the light effect is real; intent unproven
• Debated experts disagree
• Proposed single-site claim, untested
• Not supported the survey or the statistics do not support it

GrúpaíWhole classes of monument

TástálachaPre-registered tests

Following the PA Marine approach, each test is written down, with its data, null model and pass rule, before anything is scored. The tests were scored on 9 Oct 2026 with code frozen beforehand (commit c244e8f). Confirmatory tests T1 and T2 found an effect; T3 and T5 found nothing. T4 showed a signal but is listed as exploratory because that signal was seen before the freeze. Full results · Torthaí → The full protocol is in RESEARCH.md and prereg/tests_v1.json.

Feara Bréige, the Seven Monuments near Loughrea, was written down on its own before any line was measured. The published positions are not exact enough, so the card gives no alignment.

Foinsí agus ceadúnaisSources & credits

All references

Conas tagairt a dhéanamhHow to cite

If you use the map, the horizons or the test results, please cite the project and the underlying open data (see Sources). The methods, data pipeline and pre-registration are written up in Methods · RESEARCH.md.

@misc{lohan2026realt,
  author       = {Lohan, Garry},
  title        = {{PA R\'ealt} · Stone and Sky: Ireland's Neolithic and
                  Bronze Age monuments and the sky they face},
  year         = {2026},
  howpublished = {\url{https://sliothar1.github.io/pa-realt/}},
  note         = {Pre-registered tests T1--T5, code frozen at commit c244e8f.
                  Source: https://github.com/Sliothar1/pa-realt}
}